"Most people would be surprised to discover that their last seafood meal may have been raised on a farm, not caught at sea," said Dr. Rebecca Goldburg, lead author of the report. "Fish and shellfish are now farmed in every state and US territory, and aquaculture is the fastest growing segment of US agriculture. Consumers should be aware of the potential environmental problems resulting from aquaculture before their next trip to the grocery store."

Declines in many wild fish populations and growing demand for seafood have made aquaculture the source of an increasing percentage of seafood in the US and throughout the world. Although precise figures are not available, virtually all the catfish and rainbow trout, roughly half the shrimp, and approximately one-third of the salmon consumed in this country are raised by fish farmers. About 25% of all the fish consumed by humans worldwide is now farmed.

Unfortunately, the growth of the fish farming industry has often come at a price to the environment. Most large US fish farms are aquatic feedlots. Similar to other forms of intensive animal production, such as hog and poultry farms, they can produce large quantities of polluting wastes. Unlike wastes from terrestrial feedlots, however, aquaculture wastes are often directly released to natural bodies of water. These wastes have the potential to contribute to current problems from nutrient pollution, such as recent outbreaks of the toxic microbe Pfeisteria, which some experts believe are linked to wastes from hog and poultry farms.

Aquaculture is often promoted as a way to reduce over-fishing, but aquaculture can actually result in a net loss of fish protein. Many farmed fish, such as salmon, trout, and shrimp, are wholly or partly carnivorous. Feeding them can require catching more fish from the ocean than are ultimately produced on the farms. "Farming carnivores such as salmon is a bit like farming tigers," said Goldburg. "About three to five pounds of wild fish are required to produce one pound of farmed salmon."

"Aquaculture need not harm the environment, however, and some forms of fish farming are inherently less polluting than others," said Goldburg. "For example, farming of filter-feeders such as clams, oysters, and other mollusks actually cleans the water. Farming of herbivorous fish such as catfish does not result in a net loss of fish protein because feed for these fish is largely made from soybeans and other crops. Moreover, there are a number of technologies and practices now being used by some fish farmers that reduce or even eliminate environmental problems caused by aquaculture."